The overall objectives of this research program are (1) to develop and validate new methods for studying the enterohepatic circulation of bile acids in man in health and disease; (2) to characterize bile acid metabolism in health and selected diseases; (3) to develop new diagnostic tests for altered bile acid metabolism; (4) to explore poorly understood areas of the enterohepatic circulation. Goals for the current year include (1) development of improved methodology (new labeled bile acids, improved techniques for solvolysis and isolation of bile acids from serum, a new radioimmunoassay for chenodeoxycholyl conjugates); (2) further characterization of the enterohepatic circulation of the steroid and amino acid moieties in man; (3) collaborative studies on patients receiving chenodeoxycholic acid for gallstone dissolution (pharmacology of chenodeoxycholic acid, in vitro studies on kinetics of cholesterol dissolution); and (4) miscellaneous studies (fat maldigestion, biliary copper secretion). BIBLIOGRAPHIC REFERENCES: Hoffman, N.E., LaRusso, N.F., and Hofmann, A.F.: Sampling intestinal content with a sequestering capsule: a non-invasive technique for determining bile acid kinetics. Mayo Clin. Proc. 51:171-175, 1976. Cowen, A.E., Hofmann, A.F., Hachey, D.L., Thomas P.J., Belobaba, D.T.E., Klein, P.D., and Tokes, L.: Synthesis of 11,12-2H2- and 11,12-3H2-labeled chenodeoxycholic and lithocholic acids. J. Lipid Res. 17:231-238, 1976.